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See detailHigh spatial resolution of late-Holocene human activities in the moist forests of central Africa using soil charcoal and charred botanical remains
Morin, Julie ULg; Biwolé, Achille; Gorel, Anaïs ULg et al

in Holocene (in press)

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities ... [more ▼]

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities have hardly been investigated with satisfactory accuracy. In this study, we propose to characterize past human activities at local scale by using a systematic quantitative and qualitative methodology based on soil charcoal and charred botanical remains. A total of 88 equidistant test-pits were excavated along six transects in two contrasting forest types in southern Cameroon. Charred botanical remains were collected by water-sieving and sorted by type (wood charcoals, oil palm endocarps, and unidentified seeds). A total of 50 Accelerator Mass Spectrometry 14C dates were also obtained. Results showed that charred macroremains were found at multiple places in the forest, suggesting scattered human activities, which were distributed into two main periods (Phase A: 2300-1300 BP – Phase B: 580 BP to the present). Charred botanical remains indicated two types of land use: (i) domestic, with oil palm endocarps most often associated with potsherds (villages) and (ii) agricultural, with charcoal as probable remnant of slash-and-burn cultivation (fields). Oil palm endocarp abundance decreased with distance from the identified human settlements. Our methodology allowed documenting, at high resolution, the spatial and temporal patterns of human activities in central African moist forests and could be applied to other tropical contexts. [less ▲]

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See detailEnrichment of Central African logged forests with high-value tree species: testing a new approach to regenerating degraded forests
Doucet, Jean-Louis ULg; Daïnou, Kasso ULg; Ligot, Gauthier ULg et al

in International Journal of Biodiversity Science, Ecosystem Services and Management (2016)

In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor ... [more ▼]

In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor both the long-term recovery of their populations and biodiversity conservation in logged forests. In this study, we analyzed the survival and growth of 23 species in plantations. Fourteen 0.2–1.1 ha mixed species plantations consisting of single-species 15 × 15 m blocks were studied for 5 years in a logging concession of southeastern Cameroon. The plantation design considered both species light requirements and sensitivity to damage by pests. To identify the best species for enrichment planting, we assessed both species performance and plantation costs. We also tested for relationships between species traits and species performance. Mean annual diameter growth increments ranged from 1.67 to 42.9 mm. No significant relationship was found between growth and survival. Herbivory by wild Bovidae was the main cause of mortality and should be carefully considered in rehabilitation efforts. We found a significant negative relationship between wood density and maximum growth rate. The other traits tested were not good predictors of species performance in plantations. The two best-performing species, Triplochiton scleroxylon and Terminalia superba, could reach the minimum cutting diameter during a 30-year cutting cycle. Costs were high and mechanized site preparation is suggested to reduce them. Widespread adoption of such plantations will only occur if financial incentives or national regulations for assuring regeneration are implemented. [less ▲]

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See detailRelationships between population density, fine-scale genetic structure, mating system and pollen dispersal in a timber tree from African rainforests
Duminil, Jérôme; Daïnou, Kasso ULg; Kaviriri, D.K. et al

in Heredity (2016), 116

Owing to the reduction of population density and/or the environmental changes it induces, selective logging could affect the demography, reproductive biology and evolutionary potential of forest trees ... [more ▼]

Owing to the reduction of population density and/or the environmental changes it induces, selective logging could affect the demography, reproductive biology and evolutionary potential of forest trees. This is particularly relevant in tropical forests where natural population densities can be low and isolated trees may be subject to outcross pollen limitation and/or produce low-quality selfed seeds that exhibit inbreeding depression. Comparing reproductive biology processes and genetic diversity of populations at different densities can provide indirect evidence of the potential impacts of logging. Here, we analysed patterns of genetic diversity, mating system and gene flow in three Central African populations of the self-compatible legume timber species Erythrophleum suaveolens with contrasting densities (0.11, 0.68 and 1.72 adults per ha). The comparison of inbreeding levels among cohorts suggests that selfing is detrimental as inbred individuals are eliminated between seedling and adult stages. Levels of genetic diversity, selfing rates (∼16%) and patterns of spatial genetic structure (Sp ∼ 0.006) were similar in all three populations. However, the extent of gene dispersal differed markedly among populations: the average distance of pollen dispersal increased with decreasing density (from 200m in the high-density population to 1000m in the low-density one). Overall, our results suggest that the reproductive biology and genetic diversity of the species are not affected by current logging practices. However, further investigations need to be conducted in low-density populations to evaluate (1) whether pollen limitation may reduce seed production and (2) the regeneration potential of the species. [less ▲]

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See detailLate-Holocene tropical moist-forests of southeastern Cameroon: some insight from soil charcoal analysis
Morin, Julie ULg; Biwolé, Achille; Bourland, Nils et al

Conference (2015, August)

Tropical forests of Central Africa constitute the second most important block of moist forest of the world. Little is known, however, about past vegetation in this region that remains underexplored ... [more ▼]

Tropical forests of Central Africa constitute the second most important block of moist forest of the world. Little is known, however, about past vegetation in this region that remains underexplored (Vleminckx et al. 2014; Morin-Rivat et al. 2014). Determining the past specific composition of these forests could allow bringing insights into their evolution over time and providing data about their resilience capacity facing global change. We performed a pedoanthracological analysis in the semi-deciduous forests of southeastern Cameroon. We excavated 53 test pits of 53 50 × 50 × 60 cm in plots of botanical inventory along a NS 80-km long mega-transect that followed a vegetation gradient. We sorted and quantified charred macrobotanical remains by layers of 10 cm, then identified species from wood charcoals. We used the InsideWood database, implemented with 163 new anatomical descriptions of woods present in the study area by using the reference collection of African woods of the Royal Museum for Central Africa (Belgium). Finally, we obtained 25 radiocarbon dates on charcoals and oil palm endocarps. Results showed that repeated fire events occurred across the study area during the last 2500 years, soon after the well-documented “rainforest crisis” (e.g. Lézine et al. 2013). The analyzed charcoals are likely human-induced regarding evidence of associated human settlements (e.g. potsherds). Aged were distributed into two time periods: the Early Iron Age (2300-1300 BP) and the Late Iron Age (700-100 BP) with an intermediate hiatus in human occupation (see e.g. Wotzka 2006; Morin-Rivat et al. 2014). Specific composition during both periods did not strongly differ from current composition, which is now dominated by light-demanding canopy trees belonging to old-growth semi-deciduous Celtis forests (Gond et al. 2013; Fayolle et al. 2014). This argues in favor of the maintenance of light-demanding tree species by anthropogenic activities, such as slash-and-burn shifting cultivation. We conclude that moist forests have a good resilience capacity regarding moderate and scattered disturbances. These forests can nonetheless be deeply impacted by land-use intensification (e.g. degraded forests along roads and close to cities; Gond et al. 2013). [less ▲]

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See detailEvolutionary drivers of species delimitation in African polyploid complex trees genus Afzelia: insights from molecular phylogeny
Donkpegan, Segbedji ULg; Duminil, Jérôme; Daïnou, Kasso ULg et al

Conference (2015, July 13)

Background:. Molecular markers can improve our knowledge of the rain forest biodiversity, especially to decipher species evolution and delimitation within genera. In this study, we investigated ... [more ▼]

Background:. Molecular markers can improve our knowledge of the rain forest biodiversity, especially to decipher species evolution and delimitation within genera. In this study, we investigated evolutionary relationships among the Afzelia genus, an important tropical timber taxon in Africa.. Method: We used nuclear and chloroplast DNA associated with partial plastome sequences data to infer phylogenetic relationships among the six broadly distributed species of the genus: A. africana and A. quanzensis (savannah species), A. bipindensis, A. bella, A. pachyloba and A. parviflora (forest species). Using microsatellite markers (SSR), we also applied a clustering analysis (STRUCTURE) to verify whether the current taxonomic species delimitation matches the biological species concept. Result and discussion: Our SSR data showed for the first time that savannah species were diploid while forest species were tetraploid. Nuclear DNA separates diploid and tetraploid species in two distinct cladesbut plastid markers show that one diploid species forms a well-supported clade with the tetraploids, suggesting historical hybridization, possibly in relation with genome duplication (polyploidization) and habitat shift from dry to rain forests. The genetic structure observed with SSR confirms the taxonomic delimitation of the two diploid species and one tetraploid species (A. pachyloba). It also suggests the existence of a single Afzelia forest species in West Africa, and the presence of two distint species within the A. bipindensis taxon, with potential hybridization with A. bella. Conclusion: The evolutionary history of the genus Afzelia is complex and the potential link between polyploidization and habitat shift needs further investigation. Our data also show that species delimitation must be revisited, at least among three of the four rain forest species. [less ▲]

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See detailHigh spatial resolution of late-Holocene human activities in the moist forests of Central Africa using soil charcoal and charred botanical remains
Morin, Julie ULg; Biwolé, Achille; Gorel, Anaïs ULg et al

Conference (2015, April 27)

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities ... [more ▼]

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities have hardly been investigated with satisfactory accuracy. In this study, we propose to characterize past human activities at local scale by using a systematic quantitative and qualitative methodology based on soil charcoal and charred botanical remains. A total of 88 equidistant test-pits were excavated along six transects in two contrasting forest types in southern Cameroon. Charred botanical remains were collected by water-sieving and sorted by type (wood charcoals, oil palm endocarps, and unidentified seeds). A total of 50 Accelerator Mass Spectrometry 14C dates were also obtained. Results showed that charred macroremains were found at multiple places in the forest, suggesting scattered human activities, which were distributed into two main periods (Phase A: 2300-1300 BP – Phase B: 580 BP to the present). Charred botanical remains indicated two types of land use: (i) domestic, with oil palm endocarps most often associated with potsherds (villages) and (ii) agricultural, with charcoal as probable remnant of slash-and-burn cultivation (fields). Oil palm endocarp abundance decreased with distance from the identified human settlements. Our methodology allowed documenting, at high resolution, the spatial and temporal patterns of human activities in central African moist forests and could be applied to other tropical contexts. [less ▲]

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See detailSeed and pollen dispersal in Guineo-Congolian canopy tree species – insights from genetic markers in multiple species
Hardy, Olivier J.; Duminil, Jérôme; Daïnou, Kasso ULg et al

Conference (2015, April)

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See detailDifferential Performance between Two Timber Species in Forest Logging Gaps and in Plantations in Central Africa
Fayolle, Adeline ULg; Ouedraogo, Dakis-Yaoba ULg; Ligot, Gauthier ULg et al

in Forests (2015), 6(2), 380-394

To develop silvicultural guidelines for high-value timber species of Central African moist forests, we assessed the performance of the pioneer Milicia excelsa (iroko, Moraceae), and of the non-pioneer ... [more ▼]

To develop silvicultural guidelines for high-value timber species of Central African moist forests, we assessed the performance of the pioneer Milicia excelsa (iroko, Moraceae), and of the non-pioneer light demander Pericopsis elata (assamela, Fabaceae) in logging gaps and in plantations in highly degraded areas in south-eastern Cameroon. The survival and size of each seedling was regularly monitored in the silvicultural experiments. Differences in performance and allometry were tested between species in logging gaps and in plantations. The two species performance in logging gaps was significantly different from plantations and concurred with the expectations of the performance trade-off hypothesis but not with the expectations of species light requirements. The pioneer M. excelsa survived significantly better in logging gaps while the non-pioneer P. elata grew significantly faster in plantations. The high mortality and slow growth of M. excelsa in plantations is surprising for a pioneer species but could be explained by herbivory (attacks from a gall-making psyllid). Identifying high-value native timber species (i) with good performance in plantations such as P. elata is of importance to restore degraded areas; and (ii) with good performance in logging gaps such as M. excelsa is of importance to maintain timber resources and biodiversity in production forests. [less ▲]

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See detailHow Tightly Linked Are Pericopsis elata (Fabaceae) Patches to Anthropogenic Disturbances in Southeastern Cameroon?
Bourland, Nils; Cerisier, François; Daïnou, Kasso ULg et al

in Forests (2015), 6(2), 293-310

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and ... [more ▼]

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and-burn agriculture since 3000–2000 BP (Before Present) could be the main driver of the persistence of light-demanding tree species. In order to examine anthropogenic factors in the persistence of such populations, our study focused on Pericopsis elata, an endangered clustered timber species. We used a multidisciplinary approach comprised of botanical, anthracological and archaeobotanical investigations to compare P. elata patches with surrounding stands of mixed forest vegetation (“out-zones”). Charcoal samples were found in both zones, but were significantly more abundant in the soils of patches. Eleven groups of taxa were identified from the charcoals, most of them also present in the current vegetation. Potsherds were detected only inside P. elata patches and at different soil depths, suggesting a long human presence from at least 2150 to 195 BP, as revealed by our charcoal radiocarbon dating. We conclude that current P. elata patches most likely result from shifting cultivation that occurred ca. two centuries ago. The implications of our findings for the dynamics and management of light-demanding tree species are discussed. [less ▲]

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See detailMicrosatellite Development and Flow Cytometry in the African Tree Genus Afzelia (Fabaceae, Caesalpinioideae) Reveal a Polyploid Complex
Donkpegan, Segbedji ULg; Doucet, Jean-Louis ULg; Daïnou, Kasso ULg et al

in Applications in Plant Sciences (2015), 3(1)

Premise of the study: Microsatellites were developed in the vulnerable African rainforest tree Afzelia bipindensis to investigate gene flow patterns. Methods and Results: Using 454 GS-FLX technique, 16 ... [more ▼]

Premise of the study: Microsatellites were developed in the vulnerable African rainforest tree Afzelia bipindensis to investigate gene flow patterns. Methods and Results: Using 454 GS-FLX technique, 16 primer sets were identified and optimized, leading to 11 polymorphic and readable markers displaying each six to 25 alleles in a population. Up to four alleles per individual were found in each of the loci, without evidence of fixed heterozygosity, suggesting an autotetraploid genome. Cross-amplification succeeded for all loci in the African rainforest species A. pachyloba and A. bella, which appeared tetraploid, and for most loci in the African woodland species A. africana and A. quanzensis, which appeared diploid, but failed in the Asian species A. xylocarpa. Flow cytometry confirmed the suspected differences in ploidy. Conclusions: African Afzelia species are diploid or tetraploid, a situation rarely documented in tropical trees. These newly developed microsatellites will help in the study of their mating system and gene flow patterns. [less ▲]

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See detailLight Response of Seedlings of a Central African Timber Tree Species, Lophira alata (Ochnaceae), and the Definition of Light Requirements
Biwolé, Achille Bernard; Daïnou, Kasso ULg; Fayolle, Adeline ULg et al

in Biotropica (2015), 47(6), 681-688

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many ... [more ▼]

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many implications in forest management and restoration ecology. Most shadetolerance classification systems have been proposed based on empirical observations in a specific area and thus result in contradictions among categories assigned to a given species. In this study, we aimed to quantify the light requirements for seedling growth of a Central African timber tree, Lophira alata (Ochnaceae), taking into account effects of population origin. In two controlled experiments: a light response experiment and a comparative population experiment, conducted in southwestern Cameroon, using seeds collected from four populations (three from Cameroon and one from Gabon), we examined the quantitative responses to irradiance of seedlings. After 2 years, mortality was very low (<3%), even in extremely low irradiance. Growth and biomass allocation patterns varied in response to light, with intermediate irradiance (24–43%) providing optimal conditions. Light response differed between populations. The Boumba population in the northeastern edge of the species’ distribution exhibited the highest light requirements, suggesting a local adaptation. As a result of positive growth at low irradiance and maximum growth at intermediate irradiance, we concluded that L. alata exhibits characteristics of both non-pioneer and pioneer species. Implications of our results to propose an objective way to assign the light requirement for tropical tree species are discussed. [less ▲]

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See detailNew data on the recent history of the littoral forests of southern Cameroon: an insight into the role of historical human disturbances on the current forest composition
Biwolé, Achille ULg; Morin-Rivat, Julie ULg; Fayolle, Adeline ULg et al

in Plant Ecology and Evolution (2015), 148(1), 19-28

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they ... [more ▼]

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they were progressively concentrated in villages along roads, leaving large areas of forest derelict. In south-western Cameroon, and elsewhere in Central Africa, forest canopy is dominated by long-lived lightdemanding tree species, suggesting a possible role of human disturbance. The aim of this study was to bring new insights into the possible effect of historical human disturbances in terms of timing and spatial extent on the current forest composition. Location – Wet evergreen littoral forest in south-western Cameroon. Methods and key results – A combined vegetation sampling and archaeobotanical survey were conducted. Potsherds, oil-palm endocarps, and charcoal were found throughout the study area, suggesting generalised human occupation and anthropogenic fire. Human occupancy occurred in two periods: between 2200 and 1500 BP, and, more recently, beginning three centuries ago. High frequency of fire and the presence of Elaeis guineensis both dated recently (between 260 and 145 BP) suggest slash-and-burn shifting cultivation practices. These human-induced disturbances may coincide with the age of the current emergent lightdemanding species, the age of which can be estimated around 200 years, or with the phases of drying climate recorded in the Central African forest in the early 18th century. Conclusions – These results support the idea that historical human disturbances are one of the major factors that shaped the current forest composition in Central Africa. [less ▲]

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See detailGlobally, functional traits are weak predictors of juvenile tree growth, and we do not know why
Paine, C.E. Thimothy; Amissah, Lucy; Auge, Harald et al

in Journal of Ecology (2015), 103(4), 978-989

1. Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with ... [more ▼]

1. Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with high SLA, low wood density and small seeds tend to have faster growth rates. 2. If community-level relationships between traits and growth have general predictive value, then similar relationships should also be observed in analyses that integrate across taxa, biogeographic regions and environments. Such global consistency would imply that traits could serve as valuable proxies for the complex suite of factors that determine growth rate, and, therefore, could underpin a new generation of robust dynamic vegetation models. Alternatively, growth rates may depend more strongly on the local environment or growth–trait relationships may vary along environmental gradients. 3. We tested these alternative hypotheses using data on 27 352 juvenile trees, representing 278 species from 27 sites on all forested continents, and extensive functional trait data, 38% of which were obtained at the same sites at which growth was assessed. Data on potential evapotranspiration (PET), which summarizes the joint ecological effects of temperature and precipitation, were obtained from a global data base. 4. We estimated size-standardized relative height growth rates (SGR) for all species, then related them to functional traits and PET using mixed-effect models for the fastest growing species and for all species together. 5. Both the mean and 95th percentile SGR were more strongly associated with functional traits than with PET. PET was unrelated to SGR at the global scale. SGR increased with increasing SLA and decreased with increasing wood density and seed mass, but these traits explained only 3.1% of the variation in SGR. SGR–trait relationships were consistently weak across families and biogeographic zones, and over a range of tree statures. Thus, the most widely studied functional traits in plant ecology were poor predictors of tree growth over large scales. 6. Synthesis. We conclude that these functional traits alone may be unsuitable for predicting growth of trees over broad scales. Determining the functional traits that predict vital rates under specific environmental conditions may generate more insight than a monolithic global relationship can offer. [less ▲]

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See detailThe role of great apes in seed dispersal of the tropical forest tree species Dacryodes normandii (Burseraceae) in Gabon
Haurez, Barbara ULg; Daïnou, Kasso ULg; Tagg, Nikki et al

in Journal of Tropical Ecology (2015), 31(05), 395-402

The identification of seed dispersers and predators is essential to understand the effect of anthropogenic disturbances, and the associated defaunation process, on tropical forest dynamics in Central ... [more ▼]

The identification of seed dispersers and predators is essential to understand the effect of anthropogenic disturbances, and the associated defaunation process, on tropical forest dynamics in Central Africa. In this study, the animals involved in seed predation and dispersal of Dacryodes normandii (Burseraceae), an endozoochorously dispersed tree species endemic to Gabonese forests, were identified in a site in south-east Gabon using two complementary methods: direct observation and camera-trap monitoring of fruit piles. The combined sampling effort (172 h of direct observations and 796 d of camera trapping) led to the identification of six disperser and eight predator species of D. normandii seeds. With high frequency of consumption (88% and 57% of their visits, respectively) and long visit duration (83 and 23 min, respectively), the western lowland gorilla and central chimpanzee were identified as the main dispersers of this species. Seeds passed through the gorilla gut exhibited high germination success (68%). Rodents were identified as predators of D. normandii seeds, potentially displaying rare secondary dispersal through scatter-hoarding. The results of this study highlight the importance of great apes in the seed dispersal of this tree species. [less ▲]

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See detailLe genre Guibourtia Benn., un taxon à haute valeur commerciale et sociétale (synthèse bibliographique)
Tosso, Dji-ndé Félicien ULg; Daïnou, Kasso ULg; Hardy, J. Olivier et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2015), 19(1),

Known as a genus of great socio-cultural and economical importance, Guibourtia Benn. includes morphologically very similar multipurpose sister species, found in various habitats with different climate and ... [more ▼]

Known as a genus of great socio-cultural and economical importance, Guibourtia Benn. includes morphologically very similar multipurpose sister species, found in various habitats with different climate and soil conditions. In many places, Guibourtia is subject to local overexploitation by forest companies and local communities. As the population density of Guibourtia species is generally very low, it may be necessary to conduct scientific investigations that will provide valuable information for the management of the populations concerned. This paper is based on an extensive literature review and summarizes the available information on the genus Guibourtia, in terms of botany, ecology, genetics, forestry and ethnobotany. Our review provided evidence that, to date, ecological and silvicultural knowledge regarding Guibourtia species is lacking and that it is very difficult to morphologically differentiate very similar sister species. In addition, we provide a new determination key for the genus Guibourtia. Based on the available information, it is difficult to assess the conservation status of these taxa. Further investigations are needed to suggest appropriate management strategies for Guibourtia. Moreover, species diversity within this genus and its distribution in various tropical biomes make it an excellent biological model for understanding the historical, biological and environmental mechanisms that explain the diversity of tropical moist forests. [less ▲]

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See detailEnrichment of Logging Gaps with a High Conservation Value Species (Pericopsis elata) in a Central African Moist Forest
Ouedraogo, Dakis-Yaoba ULg; Fayolle, Adeline ULg; Daïnou, Kasso ULg et al

in Forests (2014), 5(12), 3031-3047

In central Africa, most of the timber species require high light at the seedling stage for survival and growth. Forest managers face a regeneration shortage of these light-demanding timber species. To ... [more ▼]

In central Africa, most of the timber species require high light at the seedling stage for survival and growth. Forest managers face a regeneration shortage of these light-demanding timber species. To achieve long-term sustainability, there is a need for enrichment methods combining low cost and high species performance. The aim of this study was to assess the performance of Pericopsis elata seedlings in enriched logging gaps in Cameroon. Over five years; the survival and size of each seedling was monitored in 27 logging gaps that were either left without maintenance or cleared. Gaps were relatively small with an average total area of 155 m2. We found that planted seedlings of P. elata performed well in logging gaps. Even without any maintenance 61% of the planted seedlings survived after five years with an average annual diameter increment of 0.28 cm. P. elata appeared to be a good candidate species for enrichment in logging gaps. We demonstrated that the seedlings of P. elata tolerated a wide range of soil conditions but that their performance was strongly influenced by light availability (gap clearance), suggesting potentially improved performance of P. elata in high light environments such as in plantation or larger gaps. [less ▲]

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See detailSoil charcoal to assess the impacts of past human disturbances on tropical forests
Vleminckx, Jason; Morin-Rivat, Julie ULg; Biwolé, Achille et al

in PLoS ONE (2014), 9(11),

The canopy of many central African forests is dominated by light-demanding tree species that do not regenerate well under themselves. The prevalence of these species might result from ancient slash-and ... [more ▼]

The canopy of many central African forests is dominated by light-demanding tree species that do not regenerate well under themselves. The prevalence of these species might result from ancient slash-and-burn agricultural activities that created large openings, while a decline of these activities since the colonial period could explain their deficit of regeneration. To verify this hypothesis, we compared soil charcoal abundance, used as a proxy for past slash-and-burn agriculture, and tree species composition assessed on 208 rainforest 0.2 ha plots located in three areas from Southern Cameroon. Species were classified in regeneration guilds (pioneer, non-pioneer light-demanding, shade-bearer) and characterized by their woodspecific gravity, assumed to reflect light requirement. We tested the correlation between soil charcoal abundance and: (i) the relative abundance of each guild, (ii) each species and family abundance and (iii) mean wood-specific gravity. Charcoal was found in 83% of the plots, indicating frequent past forest fires. Radiocarbon dating revealed two periods of fires: ‘‘recent’’ charcoal were on average 300 years old (up to 860 BP, n = 16) and occurred in the uppermost 20 cm soil layer, while ‘‘ancient’’ charcoal were on average 1900 years old (range: 1500 to 2800 BP, n = 43, excluding one sample dated 9400 BP), and found in all soil layers. While we expected a positive correlation between the relative abundance of light demanding species and charcoal abundance in the upper soil layer, overall there was no evidence that the current heterogeneity in tree species composition can be explained by charcoal abundance in any soil layer. The absence of signal supporting our hypothesis might result from (i) a relatively uniform impact of past slash-and-burn activities, (ii) pedoturbation processes bringing ancient charcoal to the upper soil layer, blurring the signal of centuries-old Human disturbances, or (iii) the prevalence of other environmental factors on species composition. [less ▲]

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See detailAnalyse à haute résolution spatiale et temporelle des activités humaines à l’Holocène récent dans les forêts humides d’Afrique Centrale
Morin, Julie ULg; Gorel, Anaïs ULg; Biwolé, Achille et al

Poster (2014, November)

Des études paléoécologiques et archéologiques ont démontré que les populations humaines ont de longue date investi les forêts humides d’Afrique Centrale. Les occupations humaines ont toutefois été peu ... [more ▼]

Des études paléoécologiques et archéologiques ont démontré que les populations humaines ont de longue date investi les forêts humides d’Afrique Centrale. Les occupations humaines ont toutefois été peu documentées en raison de difficultés relatives à l’accès au terrain. Nous présentons ici une méthodologie systématique basée sur la quantification et la datation des macrorestes botaniques carbonisés pour définir les activités humaines passées en forêt tropicale africaine. Pour cela, 53 sondages équidistants ont été creusés dans 3 sites du sud-est-du Cameroun. Dans chaque sondage ont été prélevées des quantités fixes de sol par couche de 10 cm. Les macrorestes botaniques carbonisés ont été récoltés par tamisage à l’eau directement sur le site. Les refus de tamis ont été triés (charbons de bois, endocarpes de palmier à huile, graines non identifiées), pesés sur une balance de précision et analysés statistiquement. En outre, 25 échantillons ont été datés par AMS. Les résultats montrent que les activités humaines sont réparties en deux périodes : l’âge du Fer ancien entre 2300 et 1300 BP et l’âge du Fer récent entre 670 BP et l’actuel. En outre, les charbons de bois et les endocarpes de palmier à huile ne représentent pas le même type d’activités. Deux villages âge du Fer ancien datés d’environ 2000 BP ont été identifiés par la présence concomitante d’endocarpes de palmier à huile et de tessons céramiques. Les motifs circulaires imprimés dans la céramique et inédits pour la zone d’étude rappellent les gravures et décors céramiques découverts au Gabon et dans la zone de la Sangha-Likwala-aux-Herbes, datés également de 2000 BP. L’abondance décroissante des charbons dans l’orbe d’influence de ces villages pourrait correspondre à d’anciennes zones agricoles. Les perturbations les plus récentes peuvent, quant à elles, être mises en relation avec la végétation actuelle, en particulier les arbres émergents héliophiles qui dominent la composition floristique et qui sont des recrus post-culturaux. Pour la première fois, une méthodologie quantitative basée sur les restes archéobotaniques a été appliquée en Afrique Centrale. Elle nous a permis de documenter à haute résolution la répartition spatiale et temporelle des activités humaines à l’échelle locale. Ce travail sera poursuivi par une reconstitution paléoenvironnementale à partir de l’identification des macrorestes végétaux. [less ▲]

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See detailKnowing the past to anticipate the future: soil charcoal as a proxy to model forest evolution
Morin, Julie ULg; Biwolé, Achille; Bourland, Nils et al

Poster (2014, October)

Tropical forests of Central Africa constitute the second most important block of moist forest of the world. However little is known about their past evolution. Indeed, determining the past specific ... [more ▼]

Tropical forests of Central Africa constitute the second most important block of moist forest of the world. However little is known about their past evolution. Indeed, determining the past specific composition of these forests could allow modeling their evolution over time and providing data about their resilience capacity facing global change. To do this, we performed a pedoanthracological analysis in the semi-deciduous forests of southeastern Cameroon. We excavated test pits in 53 plots of botanical inventory along a gradient of vegetation, quantified wood charcoals by layers of 10 cm, identify the species present in charcoals, dated the charcoals by the radiocarbon method, then built up sequences including present forest composition. Results show that repeated fire events occurred across the study area during the last 2500 years. These disturbances are likely human-induced regarding evidence of anthropogenic activities (e.g. potsherds). Nonetheless the past specific composition does not strongly differ from the current one except for the oldest layers related to the major dry climatic event of 2500 BP. We conclude that moist forests have a good resilience capacity regarding moderate disturbances but were and will be deeply impacted by climate change. [less ▲]

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